Byte Masking - GameCreators Forum

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revenant chaos

DBPro Master

19

Years of Service

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Joined: 21st Mar 2007

Location: Robbinsdale, MN

Posted: 31st Mar 2011 23:51

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Let's say I wanted to write a system similar to DBPro's camera masking commands, How would I go about determining the values which went onto said mask. Here is what I have tried:

+ Code Snippet

CamMask=(1^2)||(2^2)||(3^2)  `cameras 1+2+3

for Cam=1 to 32
	//See if the camera was included in the mask
	CamIncluded=CamMask && (Cam^2)
	if CamIncluded>0
		print "Camera ",Cam," Was Included in the mask!!"
	endif	
next Cam

wait key

But as you can see, It does not work as I expected. I am new to the whole bit-wise operation thing so what am I missing/doing wrong?

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bitJericho

23

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Joined: 9th Oct 2002

Location: United States

Posted: 1st Apr 2011 00:16 Edited at: 1st Apr 2011 00:24

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Here's a tutorial for bitflags.

http://weblogs.asp.net/wim/archive/2004/04/07/109095.aspx

Actually, that's a pretty confusing example. Here's some simple code

+ Code Snippet

   #constant check1 = 1
   #constant check2 = 2
   #constant check3 = 4
   #constant check5 = 8

   value_to_test = 9

   If (value_to_test & check1) = check1 
     print "Set!"
   Else 
     print "Not set!"
   EndIf 
   If (value_to_test & check2) = check2
     print "Set!"
   Else 
     print "Not set!"
   EndIf 
   If (value_to_test & check3) = check3
     print "Set!"
   Else 
     print "Not set!"
   EndIf 
   If (value_to_test & check4) = check4
     print "Set!"
   Else 
     print "Not set!"
   EndIf

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Neuro Fuzzy

19

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Joined: 11th Jun 2007

Location:

Posted: 1st Apr 2011 00:45 Edited at: 1st Apr 2011 00:48

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Quote: "CamMask=(1^2)||(2^2)||(3^2) `cameras 1+2+3

for Cam=1 to 32
//See if the camera was included in the mask
CamIncluded=CamMask && (Cam^2)
if CamIncluded>0
print "Camera ",Cam," Was Included in the mask!!"
endif
next Cam

wait key
"

Actually... What you really want to do is this:

+ Code Snippet

CamMask=1|(1<<1)|(1<<2)

From the rightmost bit, the Nth bit to the left of it IS NOT n^2, but 1*2^n. So 1|2|4|8=(1111 base 2)
[edit]
Also, I think 1||2=1, because that's BOOLEAN "or", not bitwise "or". With dbpro, I think a number greater than 0 is true, and 0 is false.

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IanM

Retired Moderator

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Joined: 11th Sep 2002

Location: In my moon base

Posted: 1st Apr 2011 21:29

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DBPro doesn't have a boolean OR - it has bit-wise only, so using || is correct.

As you've pointed out, the problem was the 'Cam^2' - that should have been '2^Cam' instead. The exact same problem exists in the first line of the code too.

+ Code Snippet

CamMask = (2^1) || (2^2) || (2^3)

for Cam = 1 to 32
    //See if the camera was included in the mask
    CamIncluded=CamMask && (2^Cam)
    if CamIncluded>0
        print "Camera ",Cam," Was Included in the mask!!"
    endif    
next Cam

wait key

You can also generate and test the mask using << and >> instead

+ Code Snippet

CamMask = (1 << 1) || (1 << 2) || (1 << 3)

for Cam = 1 to 32
    //See if the camera was included in the mask
    CamIncluded = (CamMask >> 1) && 1
    if bit get( CamMask, Cam )
        print "Camera ",Cam," Was Included in the mask!!"
    endif    
next Cam

wait key

Finally, there are also some bit commands in my plug-in set that can also be used instead of the bitwise&power operators:

+ Code Snippet

CamMask = bit set( CamMask, 1 )     ` Camera 1
CamMask = bit set( CamMask, 2 )     ` Camera 2
CamMask = bit set( CamMask, 5 )     ` Camera 5


for Cam = 1 to 32
    //See if the camera was included in the mask
    if bit get( CamMask, Cam )
        print "Camera ",Cam," Was Included in the mask!!"
    endif    
next Cam

wait key

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